1. Field of the Invention
The present invention relates to a magnetic tape device including a roller guide to guide a magnetic tape as the magnetic tape travels past a magnetic head to perform reading/writing of data with respect to the magnetic tape. The roller guide comprises a shaft mountable on a base; an upper flange unit disposed in an upper portion of the shaft and moveable in an up and down direction, the upper flange unit having a lower surface in sliding contact with an upper edge of the magnetic tape; a coil spring to urge the upper flange unit downward; a lower flange unit disposed in a lower portion of the shaft, the lower flange unit having an upper surface in sliding contact with a lower edge of the magnetic tape; and a roller unit having the magnetic tape wrapped on an outer circumferential surface, wherein the roller unit is coaxial with the shaft between the upper flange unit and the lower flange unit, and rotates accompanying to the travel of the magnetic tape.
Moreover, the present invention relates to a magnetic tape device including a tape guide having a roller guide and a guide post to guide a magnetic tape as the magnetic tape travels past a magnetic head to perform reading/writing of data with respect to the magnetic tape. The roller guide comprises a shaft; an upper flange unit disposed on an upper portion of the shaft, the upper flange unit having a lower surface in sliding contact with an upper edge of the magnetic tape; a lower flange unit disposed on a lower portion of the shaft, the lower flange unit having an upper surface in sliding contact with a lower edge of the magnetic tape; and a roller unit having the magnetic tape wrapped around an outer circumference, wherein the roller unit is coaxial with the shaft between the upper flange unit and the lower flange unit, and rotates accompanying the travel of the magnetic tape. The guide post comprises an upper flange unit disposed on an upper portion of the shaft, the upper flange unit having a lower surface in sliding contact with an upper edge of the magnetic tape; a lower flange unit disposed on a lower portion of the shaft, the lower flange unit having an upper surface in sliding contact with a lower edge of the magnetic tape; and a sliding contact portion having the magnetic tape wrapped around an outer circumferential surface located coaxially with the shaft between the upper flange unit and the lower flange unit and in sliding contact with the magnetic tape.
2. Description of the Related Art
A conventional magnetic tape device performs reading of data from a magnetic tape and writing of data to the magnetic tape with a magnetic head as the magnetic tape travels past the magnetic head. The magnetic tape is guided as it travels by a tape guide consisting of roller guides, or consisting of roller guides and guide posts.
FIG. 15 is a cross sectional diagram of a roller guide used in a prior art magnetic tape device. As shown in FIG. 15, the roller guide consists of a cylindrical shaft 1 set up on a base (not shown). The cylindrical shaft 1 includes a large diameter portion 1A integrally formed in a lower portion of the shaft 1. A lower flange unit 3, made of ceramic or the like, is integrally adhered to an upper surface of the large diameter portion 1A. An upper surface of the lower flange unit 3 is formed as a flat surface, and the lower edge of the magnetic tape is in sliding contact with the upper surface of the lower flange unit 3. Furthermore, a convex portion 1B is formed in a lower end of the shaft 1, and a screw hole 1C is formed in a lower surface of the convex portion 1B for fixing the roller guide to the base.
A roller portion 6 having a cylindrical form is supported, coaxially with the center portion of the shaft 1, by an upper bearing 4 and a lower bearing 5. The roller portion 6 rotates with the magnetic tape in contact with its outer circumferential surface.
Moreover, an upper flange unit 8 is disposed on an upper portion of the shaft 1 fitted to a holder 7 having a flanged cylindrical form, and is movable in the shaft direction (up and down direction). More particularly, as shown in FIG. 15, the holder 7 is fitted to the upper portion of the shaft 1, and the upper flange unit 8 is fitted to the cylindrical portion of the holder 7 such that the upper flange unit 8 is movable in the shaft direction. A lower surface of the upper flange unit 8 is formed as a flat surface, and the upper edge of the magnetic tape is in sliding contact with the lower surface of the upper flange unit 8. Furthermore, a cap 10 is fixed to the upper end surface of the shaft 1 with a small flat head screw (bolt) 9.
A compression coil spring 11 is inserted between an inner ring of the upper bearing 4 and the holder 7. A ring 12 is located between an inner ring of the lower bearing 5 and a step portion of the shaft 1. The action of the compression coil spring 11 takes up the play of the upper and lower bearings 4, 5 in the shaft direction, thereby taking up the play of the roller 6 in the up and down direction.
A compression coil spring 13 is also inserted between the upper flange unit 8 and the cap 10. The action of the compression coil spring 13 urges the upper flange unit 8 toward the lower flange unit 3, and the magnetic tape which travels between the upper flange unit 8 and the lower flange unit 3 is normally pressed against the lower flange unit 3. Accordingly, the magnetic tape travels while the upper and lower edges of the magnetic tape are in sliding contact with the lower surface of the upper flange unit 8 and the upper surface of the lower flange unit 3, respectively. Moreover, the travel height of the magnetic tape is determined by the position (height) of the lower flange unit 3.
FIG. 16 is a diagram showing a prior art magnetic head assembly including a roller guide having the construction shown in FIG. 15. As shown in FIG. 16, roller guides 21, 22 are positioned in a line on a base 23 in a direction of travel of the magnetic tape. The roller guides 21, 22 include lower flange units 21A, 22A, respectively. Step holes 23A, 23B are drilled in the base 23, and the convex portions (corresponding to 1B in FIG. 15) of the roller guides 21, 22 are fitted into the step holes 23A, 23B, respectively. After the convex portions are fitted into step holes 23A, 23B, small screws (bolts) 24A, 24B are screwed into screw holes (corresponding to IC in FIG. 15) from below, thereby fixing the respective roller guides 21, 22 to the base 23.
A magnetic head assembly 25 is fixed to the base between the roller guides 21, 22 with small screws (bolts) 26. As shown in FIG. 16, the magnetic head assembly 25 includes a magnetic head having a read gap GR and a write gap GW, and a plurality of heads whose number is optionally selected (for example, twenty-four) to perform reading/writing of the magnetic tape. More specifically, the magnetic head assembly 25 includes a plurality of playback head portions 27 and recording head portions 28, each corresponding to a track of the magnetic tape.
Japanese Laid-Open Patent Publication JP-A-6-60496 discloses a prior art magnetic tape device having a roller guide which is different from the roller guide shown in FIG. 15. More particularly, the magnetic tape device disclosed in Japanese Laid-Open Patent publication JP-A-6-60496 includes a roller guide having an upper flange unit and a lower flange unit having a spacing between a lower edge of the upper flange unit and an upper edge of a lower flange unit which is different when recording and playing back the magnetic tape, in comparison with when rewinding the magnetic tape. In the case of recording and playing back the magnetic tape, the spacing of the lower edge of the upper flange unit and the upper edge of the lower flange unit is narrow and the control of the height of the magnetic tape is accurately performed. In the case of rewinding the magnetic tape, the spacing is wide because the up and down movement of the magnetic tape is large during high speed travel of the magnetic tape, and the magnetic tape is exposed to excessive compressive forces.
More particularly, to make the spacing of the lower surface of the upper flange unit and the upper surface of the lower flange unit large in a fixed angular range, a guide surface having a difference in level of a top surface and a bottom surface is formed in the lower surface of the upper flange unit. By rotating the whole roller guide by a predetermined angle, the edge of the magnetic tape can be selectively placed in sliding contact with the higher or lower guide surface.
The above-described conventional magnetic tape devices relate to guiding a magnetic tape using roller guides only. However, magnetic tape devices are known wherein the magnetic tape travels while guided by a tape guide consisting of roller guides and guide posts. The roller guide used in the magnetic tape device having a tape guide consisting of roller guides and guide posts may be the same as the roller guide described above with respect to FIG. 15. Alternatively, the roller guide may be similar to the roller guide shown in FIG. 15, while eliminating the up and down movement mechanism portion of the upper flange unit, the urging action of the coil spring 13, and the like.
The guide post used in the conventional tape guide generally consists of an upper flange unit disposed in an upper portion of the shaft, the upper flange unit having a lower surface in sliding contact with the upper edge of the magnetic tape, and a lower flange unit disposed in a lower portion of the shaft, the lower flange unit having an upper surface in sliding contact with the lower edge of the magnetic tape. A sliding contact portion coaxial with the shaft and located between the upper flange unit and the lower flange unit makes sliding contact with a magnetic tape wrapped on its outer circumferential surface. The lower flange unit of the roller guide and the lower flange unit of the tape guide are separate members.
FIG. 17 is a schematic diagram illustrating the sliding contact state of the magnetic tape T and the lower flange unit 3 in the roller guide shown in FIG. 15. As shown in FIG. 17, the lower edge of the magnetic tape T is in a state of contact with an outer circumferential surface of the roller unit 6 in a wrap portion L.sub.1, which corresponds to a region of the angle of wrap .theta..sub.1. Further, the magnetic tape T is in sliding contact with the upper surface of the lower flange unit 3 in the wrap portion L.sub.1 and in non-wrap portions L.sub.2, L.sub.3, which correspond to the respective regions of the angles of wrap .theta..sub.2, .theta..sub.3.
Similarly, the upper edge of the magnetic tape T is in sliding contact with the lower surface of the upper flange unit 8 in both the wrap portion L.sub.1 and in the non-wrap portions L.sub.2, L.sub.3. The wrap portion L.sub.1 of the magnetic tape T does not receive a compressive force in the up and down direction (i.e., a bending direction) from the upper flange unit 8 and the lower flange unit 3 because the wrap portion L.sub.1 contacts the outer circumferential surface of the roller unit 6. However, the non-wrap portions L.sub.2, L.sub.3 of the magnetic tape T receive compressive forces from the upper flange unit 8 and the lower flange unit 3, and the magnetic tape becomes bent because the non-wrap portions L.sub.2, L.sub.3 are not in contact with the outer circumferential surface of the roller unit 6. The bending of the non-wrap portions L.sub.2, L.sub.3 causes poor contact (head touch) between the magnetic tape T and the magnetic head and causes reading/writing errors close to the upper and lower tape edges.
When the roller guide disclosed in Japanese Laid-Open Patent Publication JP-A-6-60496 is used during playback and recording, the interval between the lower surface of the upper flange unit and the upper surface of the lower flange unit is narrowed. However, the sliding contact of the upper edge of the magnetic tape T on the lower surface of the upper flange unit, and the sliding contact of the lower edge of the magnetic tape T on the upper surface of the lower flange unit are the same as for the roller guide shown in FIG. 17, not only in the wrap portion but also in the non-wrap portions. As a result, even when using the roller guide disclosed in Japanese Laid-Open Patent Publication JP-A-6-60496, the non-wrap portion of the magnetic tape receives compressive forces from the lower flange unit and upper flange unit in the up and down direction, and becomes bent as a result of these forces. Furthermore, the bending of the magnetic tape causes poor contact between the magnetic tape and the magnetic head close to the upper and lower tape edges, and, as a result, reading/writing errors occur.
Furthermore, in the conventional magnetic tape device having a tape guide consisting of roller guides and guide posts to guide the magnetic tape as the magnetic tape travels, the lower flange unit of the roller guide and the lower flange unit of the guide post are different members. Since the two flange units are different members, a troublesome adjustment is necessary to adjust the height of the upper surface of the two flange units, resulting in an increase in the cost of the device. Furthermore, in practice, accurate adjustment of the height of the two flange units is difficult.
Moreover, since the roller guide and the guide post are located close together, when there is a difference in level between the roller guide and the guide post, an excessive force is applied to the edge of the magnetic tape. As a result of the excessive force applied to the edge of the magnetic tape, the magnetic tape becomes bent, there is poor contact between the magnetic tape and the magnetic head, and reading/writing errors occur close to the upper and lower tape edges.